Abstract
Hereditary diffuse gastric cancer (HDGC) is an autosomal dominant condition caused by a mutation in the tumour suppressor gene E-cadherin, (CDH1). It predisposes to a 70% likelihood of developing highly penetrant diffuse gastric cancer. Because HDGC is driven by the absence of a tumour suppressor, conventional therapeutic approaches targeting tumour-promoting oncogenes cannot be used. Synthetic lethality is an approach that circumvents this issue by targeting vulnerabilities in cells that lack the functional tumour suppressor. This project aimed to investigate a potential synthetic lethal relationship between CDH1 and polo-like kinase 3 (PLK3), a cytoskeletal and cell cycle regulator.
Lentiviral delivery of two shRNA were successful in knocking down PLK3 expression in isogenic MCF10A cell lines, with and without CDH1 expression (MCF10A and CDH1-/-). Viability was measured and confirmed as synthetic lethal (mutations in combination cause cells to be less viable) if the CDH1-/- cells were less viable with a ratio of ≤0.85. Results from one shRNA knockdown trended towards synthetic lethality (p > 0.05). Another shRNA resulted with a considerable reverse synthetic lethal effect, but was not statistically significant.
PLK antagonists poloxipan and wortmannin were used to inhibit PLK3. Poloxipan induced reverse synthetic lethality with reduced viability in MCF10A cells at low concentrations. High concentrations produced a marginal synthetic lethal phenotype. Wortmannin’s effect on MCF10A and CDH1-/- cells also varied from synthetic lethal and reverse synthetic lethal.
As the viability of CDH1 deficient cells could not be significantly reduced via PLK3 knockdown or inhibition, this candidate is no longer considered to be a potential therapeutic target for the treatment of HDGC.